1. Field of the Invention
The present invention relates to inspection of a disk for defects, such as chips at the circumferential edges of the disk. More specifically, the present invention relates to inspection of a transparent disk, to be used in constructing a computer storage medium, using a laser beam.
2. Background
Digital data is often stored on a disk. For example, personal computers generally have at least one built-in disk (sometimes called a hard drive) to store digital computer data. As another example, compact disc players and DVD players read and display audio and or visual data from disks. In these applications, even a small physical defect, such as a small chip at the edge of the disk, can cause problems in reading digital data from or writing digital data to the disk.
In response to this recognized problem of physical defects at the edge of disk, disk manufacturers conventionally have a person visually inspect the edge of each disk for chips or other defects.
Although manufacturers have used laser beams to inspect the surface of a disk, these conventional inspection devices do not inspect the edge of the disk for edge chipping, largely because any data in the vicinity of the edge of the disk is used to: (1) exactly locate the disk in space with respect to the inspection device, and (2) provide baseline laser intensity data for normalizing and interpreting laser intensity data measured at locations away from the edge of the disk.
Because the data from the vicinity of the disk edge is used for disk-location and intensity calibration purposes, this data cannot be used by conventional inspection devices to determine whether defects exist at a disk""s circumferential edges. These conventional inspection machines do not generally inspect for physical defects closer than 1 mm to the circumferential edge or circumferential chamfer of the disk.
According to a primary aspect of the present invention, a disk inspection device for inspecting the circumferential edge of a disk includes a beam generator, a disk holder and a radiation detector. The beam generator generates a beam of electromagnetic radiation. The disk holder holds the disk, so that the beam will intersect the disk at an intersection zone, with the intersection zone being sufficiently close to the circumferential edge so that at least a portion of the intersection zone will overlap at least a portion of any defect in the disk. The radiation detector detects at least a portion of radiation from the beam after the beam has intersected the disk. This detected radiation can be used to determine whether the disk edge is intact and correctly shaped.
As used herein, the word xe2x80x9cdefectxe2x80x9d means any irregularity that yields a disk unsuitable for commercial use.